Organometallic Chemical Vapor Deposition of Palladium under Very Mild Conditions of Temperature in the Presence of a Low Reactive Gas Partial Pressure

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The intramolecular dynamics of a rigid yet twisty 'Ferrocenyl' TetraPhosphine : served with some 31P-NMR delicacy

Polydentate ferrocenyl phosphines equipped with bulky functional groups are regarded as rigid ligands capable of stabilizing and/or activating a broad range of chemical compounds such as smaller complexes (being formed e.g. in transition metal-catalyzed cross coupling reactions), nanoparticles, or even larger surfaces. The fruitful rigidity of these fascinating molecular species originates from the internal steric constraints imposed by the substituents; hence, the rotational reorientation of the Cp rings around the vertical 5-fold symmetry axis is hampered, and a permanent polydentate phosphine ‘cage’ is created (see figure). Latter construction then provides a large variety of coordination modes for the actual substrate what is the core structural feature being responsible for the diverse applicability spectrum. If such ferrocenyl phosphine is investigated on a sufficiently long i.e. ‘NMR time scale’ however, its decelerated intramolecular motions might be discovered and quantitatively characterized. Indeed, selective 1D 31P-{1H} EXSY {Exchange Spectroscopy} pointed out the exchange of the chemically distinct phosphoruses (green and red spheres below) in the scrutinized Fc(P)4tBu ligand and thus successfully demonstrated the previously unknown rotation (i.e. antiparallel twisting) of the Cp rings around the Fe centre. Series of measurements performed at different temperatures enabled the evaluation of the respective thermodynamic parameters (ΔS#, ΔH#, ΔG#) for which the influence of the solvent was also studied – while the confrontation of the experimental and theoretical values computed by DFT methods completed the analysis of the motion. In fact, the four 31P-s of Fc(P)4tBu composes an AA’BB’ spin system giving rise to a puzzling second order 31P NMR spectrum. Although the respective J-couplings had already been presented reclining upon the output of in silico simulations, a side track of the current work covered the full deduction of the results by the means of a quantum mechanical approach. Besides, the internal ring rotations shed new light on the ’through space’ nature of the JAA’ coupling affecting the inner phosphoruses (red spheres). That is, the interaction showed unquenchable and endured higher ring rotation rates than its actual frequency value what highlighted the intricacy of the magnetization transfer phenomena between the two nuclei. Finally, exchange phenomena were revealed for the complexed state of the ligand as well. According to 2D 1H–1H EXSY spectra, in case of [Pd(II)Br2-Fc(P)4tBu] the familiar twisting of the cyclopentadienyl rings was complemented with the periodic transconnection of the [Pd(II)Br2-] moiety between the bidentate (-PPH2)2 sites – perfectly illustrating the possibility for multiple coordination ways offered by polydentate phosphines

Heterolytic Bond Activation at Gold: Evidence for Gold(III) H-B, H-Si Complexes, H-H and H-C Cleavage

The coordinatively unsaturated gold(III) chelate complex [(C^N-CH)Au(C6F5)]+ (1+) reacts with main group hydrides H-BPin and H-SiEt3 in dichloromethane solution at 70 °C to form the corresponding σ-complexes, which were spectroscopically characterized (C^N-CH = 2-(C6H3But)-6-(C6H4But)-pyridine anion; Pin = OCMe2CMe2O). In the presence of an external base such as diethyl ether, heterolytic cleavage of the silane H-Si bond leads to the gold hydrides [{(C^N-CH)AuC6F5}2(μ-H)]+ (2+) and (C^N-CH)AuH(C6F5) (5), together with spectroscopically detected [Et3Si-OEt2]+. The activation of dihydrogen also involves heterolytic H-H bond cleavage but requires a higher temperature ( 20 °C). H2 activation proceeds in two mechanistically distinct steps: the first leading to 2 plus [H(OEt2)2]+, the second to protonation of one of the C^N pyridine ligands and reductive elimination of C6F5H. By comparison, formation of gold hydrides by cleavage of suitably activated C-H bonds is very much more facile; e.g. the reaction of 1·OEt2 with Hantzsch ester is essentially instantaneous and quantitative at 30 °C. This is the first experimental observation of species involved in the initial steps of gold catalyzed hydroboration, hydrosilylation and hydrogenation and the first demonstration of the ability of organic C-H bonds to act as hydride donors towards gold

Observation of CH⋅⋅⋅π Interactions between Methyl and Carbonyl Groups in Proteins

Protein structure and function is dependent on myriad noncovalent interactions. Direct detection and characterization of these weak interactions in large biomolecules, such as proteins, is experimentally challenging. Herein, we report the first observation and measurement of long-range "through-space" scalar couplings between methyl and backbone carbonyl groups in proteins. These J couplings are indicative of the presence of noncovalent C-H⋅⋅⋅π hydrogen-bond-like interactions involving the amide π network. Experimentally detected scalar couplings were corroborated by a natural bond orbital analysis, which revealed the orbital nature of the interaction and the origins of the through-space J couplings. The experimental observation of this type of CH⋅⋅⋅π interaction adds a new dimension to the study of protein structure, function, and dynamics by NMR spectroscopy

Phosphorus-containing gradient (block)copolymers via RAFT polymerization and post-polymerization modification

Reversible addition‐fragmentation chain transfer (RAFT) copolymerization of styrene (St) and 4‐(diphenylphosphino)styrene (DPPS) is explored to establish the statistical distribution of the phosphine‐functional monomer within the copolymer. RAFT copolymerization of St and DPPS at a variety of feed ratios provides phosphine‐functional copolymers of low dispersity at moderate monomer conversion (Ð 60%). In all cases, the fraction of DPPS in the resulting polymers is greater than that in the monomer feed. Estimation of copolymerization reactivity ratios indicates DPPS has a strong tendency to homopolymerize while St preferentially copolymerizes with DPPS (rDPPS = 4.4; rSt = 0.31). The utility of the copolymers as macro‐RAFT agents in block copolymer synthesis is demonstrated via chain extension with hydrophilic acrylamide (N,N‐dimethylacrylamide (DMAm)) and acrylate (poly(ethylene glycol) methyl ether acrylate (mPEGA), and di(ethylene glycol) ethyl ether acrylate (EDEGA)) monomers. Finally, access to polymers containing phosphine oxide and phosphonium salt functionalities is shown through postpolymerization modification of the phosphine‐containing copolymers

3D Ruthenium Nanoparticle Covalent Assemblies from Polymantane Ligands for Confined Catalysis

The synthesis of metal nanoparticle (NP) assemblies stabilized by functional molecules is an important research topic in nanoscience, and the ability to control interparticle distances and positions in NP assemblies is one of the major challenges in designing and understanding functional nanostructures. Here, two series of functionalized adamantanes, bis-adamantanes, and diamantanes, bearing carboxylic acid or amine functional groups, were used as building blocks to produce, via a straightforward method, networks of ruthenium NPs. Both the nature of the ligand and the Ru/ligand ratio affect the interparticle distance in the assemblies. The use of 1,3-adamantanedicarboxylic acid allows the synthesis of three-dimensional (3D) networks of 1.7–1.9 nm Ru NPs presenting an interparticle distance of 2.5–2.7 nm. The surface interaction between Ru NPs and the ligands was investigated spectroscopically using a 13C-labeled ligand, as well as theoretically with density functional theory (DFT) calculations. We found that Ru species formed during the NP assembly are able to partially decarbonylate carboxylic acid ligands at room temperature. Decarbonylation of a carboxylic acid at room temperature in the presence of dihydrogen usually occurs on catalysts at much higher temperatures and pressures. This result reveals a very high reactivity of ruthenium species formed during the network assembly. The Ru NP networks were found to be active catalysts for the selective hydrogenation of phenylacetylene, reaching good selectivity toward styrene. Overall, we demonstrated that catalyst activity, selectivity, and NP network stability are significantly affected by Ru NP interparticle distance and electronic ligand effects. As such, these materials constitute a unique set that should allow a better understanding of the complex surface chemistry in carbon-supported metal catalysts

Caracterización de las propiedades de mezclas de PC/ABS recicladas

Doble titulacióEl objetivo de este PFC ha sido de estudiar la evolución de las propiedades de dos mezclas muy diferentes de PC/ABS. Una ha sido preparada en el CCP (Centro Catalán del plástico) denominada material A y la otra es una mezcla Bayblend PC/ABS FR 2000 producida por Bayer que se denomina material B en este estudio. Las letras FR significan "Flame Retardant" (retardante de llama). Estas mezclas han sido inyectadas cinco veces cada una. Después de cada ciclo de inyección se debía guardar 50 probetas para los ensayos y triturar las otras para obtener la granza que permitía inyectar el próximo ciclo. En el estudio cada material se llama por la letra del material a que corresponde y la cifra del número de veces que ha sido inyectado. Entonces hay diez materiales de A1 hasta A5 y de B1 hasta B5. Las probetas han sido sometidas a varios ensayos de caracterización de las propiedades mecánicas y térmicas. Los ensayos que permiten de evaluar las propiedades mecánicas han sido los de resistencia a la tracción y de resistencia al impacto CHARPY. La evolución de la viscosidad ha sido seguida con la determinación del "Melt Flow Index" de cada material del estudio. La caracterización de las propiedades térmicas ha sido hecha a partir de la evolución de la temperatura VICAT con el reciclaje para los dos materiales A y B ya partir del ensayo de combustibilidad UL 94 para el material B. El UL 94 para el material A ha dado resultados poco concluyentes dado que este material no contiene agentes ignifugantes. Por eso no estaba útil de ver la evolución del comportamiento a la llama del material A. Los dos materiales tienen comportamientos muy distintos frente a los ensayos pero de manera general el reciclaje baja las propiedades mecánicas de resistencia a la tracción y al impacto, aumenta la fluidez pero casi no afecta las propiedades térmicas. Para los dos materiales A y B, hasta el tercero ciclo de inyección la disminución de las propiedades, que sea mecánica o térmica, no es muy significativa y la dispersión de los resultados es poco importante. Entonces este proyecto ha permitido de ver que el PC/ABS virgen puede aguantar tres ciclos de inyección sin perdidas notables de sus características